README.md

Minimal Linux Live

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Overview

Minimal Linux Live (MLL) is a tiny educational Linux distribution, which is designed to be built from scratch by using a collection of automated shell scripts. Minimal Linux Live offers a core environment with just the Linux kernel, GNU C library, and Busybox userland utilities. Additional software can be included in the ISO image at build time by using a well-documented configuration file.

The generated ISO image file contains Linux kernel, GNU C library compiled with default options, Busybox compiled with default options, quite simple initramfs structure and some “overlay bundles” (the default build process provides few overlay bundles). You don't get Windows support out of the box, nor you get any fancy desktop environment (refer to the Debootstrap Live project if you need minimal system with network and UI). All you get is a simple shell console with default Busybox applets, network support via DHCP and... well, that's all. This is why it's called “minimal”.

Note that by default Minimal Linux Live provides support for legacy BIOS systems. You can change the build configuration settings in the .config file and rebuild MLL with support for modern UEFI systems.

All build scripts are well organized and quite small in size. You can easily learn from the scripts, reverse engineer the build process and later modify them to include more stuff (I encourage you to do so). After you learn the basics, you will have all the necessary tools and skills to create your own fully functional Linux based operating system which you have built entirely from scratch.

You are encouraged to read the tutorial which explains the MLL build process. The same tutorial, along with all MLL source code, can be found in the ISO image structure in the /minimal/rootfs/usr/src directory.

List of related projects is available in the end of this document. If you don't find what you're looking for in MLL, perhaps you'll find it in the related projects, e.g. minimal Linux system with graphical user interface (GUI), or perhaps minimal Linux system with option to run Docker containers.

The README document and the main .config file provide extensive documentation regarding the Minimal Linux Live features.

The DAO of Minimal Linux Live - this tutorial explains step by step what you need to do in order to create your own minimalistic live Linux OS. The tutorial is based on the first published version of Minimal Linux Live.

The default build process uses some custom provided CFLAGS. They can be found in the .config file. Some of these additional flags were introduced in order to fix different issues which were reported during the development phase. However, there is no guarantee that the build process will run smoothly on your system with these particular flags. If you get compilation issues (please note that I'm talking about compilation issues, not about general shell script issues), you can try to disable these flags and then start the build process again. It may turn out that on your particular host system you don't need these flags.

Overlay bundles

Important note! Most of the overlay bundles come with no support since the build process for almost all of them is host specific and can vary significantly between different machines. Some overlay bundles have no dependencies to the host machine, e.g. the bundles which provide the DHCP functionality and the MLL source code. These bundles are enabled by default.

Minimal Linux Live has the concept of overlay bundles. During the boot process the OverlayFS driver merges the initramfs with the content of these bundles. This is the mechanism which allows you to provide additional software on top of MLL without touching the core build process. In fact the overlay bundle system has been designed to be completely independent from the MLL build process. You can build one or more overlay bundles without building MLL at all. However, some of the overlay bundles have dependencies on the software pieces provided by the MLL build process, so it is recommended to use the overlay build subsystem after you have produced the ‘initramfs’ area.

The overlay bundle system provides dependency management. If bundle ‘b’ depends on bundle ‘a’ you don't need to build bundle ‘a’ manually in advance. The bundle dependencies are described in special metadata file bundle_deps and all such dependencies are prepared automatically.

# How to build all overlay bundles.
cd minimal_overlay
./overlay_build.sh

# How to build specific overlay bundle. The example is for 'Open JDK'
# which depends on many GNU C libraries and on ZLIB. All dependencies
# are handled automatically by the overlay bundle system.
cd minimal_overlay
./overlay_build.sh openjdk

Take a look at the mll_hello overlay bundle which compiles simple C program (it prints one line in the console) and installs it properly in the MLL overlay structure.

Runtime software

Another way to add software in MLL is at runtime by using slightly modified version of static-get which is provided as additional overlay bundle. The static_get overlay bundle is not enabled by default. You can enable it in the main .config file. Here are some examples with static-get:

GraalVM

The current development version of MLL partially supports GraalVM (provided as overlay bundle). Note that GraalVM has runtime dependencies on GCC and Bash and therefore some GraalVM feature are not supported in MLL, e.g. the gu updater and almost all GVM language wrapper scripts, including the R wrappers. Nevertheless, the core GVM features work fine. Java, Python, Ruby, Node and JavaScript work in MLL/GraalVM environment. Great, isn't it! :)

BIOS and UEFI

Minimal Linux Live can be used on UEFI systems (as of version 28-Jan-2018) thanks to the systemd-boot project. There are three build flavors that you can choose from:

bios - MLL will be bootable only on legacy BIOS based systems. This is the default build flavor.

uefi - MLL will be bootable only on UEFI based systems.

both - MLL will be bootable on both legacy BIOS and modern UEFI based systems.

The generated MLL iso image is ‘hybrid’ which means that if it is ‘burned’ on external hard drive, this external hard drive will be bootable. You can use this behavior to install MLL on your USB flash device (read the next section).

The older version of Minimal Linux Live 20-Jan-2017 has experimental UEFI support and the MLL ISO image can be used on legacy BIOS based systems and on UEFI based systems with enabled UEFI shell (level support 1 or higher, see section 3.1 - Levels Of Support of the UEFI Shell specification). All newer versions of Minimal Linux Live have full UEFI support.

Installation

The build process produces ISO image which you can use in virtual machine or you can burn it on real CD/DVD. Installing MLL on USB flash drive currently is not supported but it can be easily achieved by using syslinux or extlinux since MLL requires just two files (one kernel file and another initramfs file). This applies for legacy BIOS based systems.

Another way to install MLL on USB flash drive is by using YUMI or other similar tools. This applies for legacy BIOS based systems.

Yet another way to install MLL on USB flash drive is by using the dd tool:

The USB flash device will be recognized as bootable device and you should be able to boot MLL successfully from it. If you have chosen the ‘combined’ build flavor (i.e. value both for the corresponding configuration property), then your USB flash device will be bootable on both legacy BIOS and modern UEFI based systems.

The build process also generates a compressed filesystem image file mll_image.tgz which contains everything from the initramfs area and everything from the overlay area, i.e. all overlay bundles that have been installed during the MLL build process. You can import and use the filesystem image in Docker like this:

Boot2Minc - this fork adds Mincs and as result you can run Linux containers inside MLL. One interesting Mincs feature - it provides tools which allow you to reuse alredy existing Docker containers.

K1773R's MLL - PowerPC version of Minimal Linux Live with memtester as additional software. Impressive work!

Ladiko's MLL - this fork automatically downloads and uses the latest available Kernel and Busybox sources. By default there is NTFS and SquashFS support. The fork also provides an installer which can be used to put MLL on USB flash device.